Denys-Drash (DDS) is a rare human condition in which severe urogenital abnormalities result nephropathy, streak gonads, ambiguous genitalia, male pseudohermaphroditism and Wilms' tumor. The condition affects mostly XY individuals. DDS patients show large variability in the extent of the genital abnormalities some have both Mullerian- and Wolffian-derived structures, and others have neither. Missense mutation in the zinc-finger region of the WT1 gene is a critical event in the elaboration of DDS. One of the most prominent mutational hot spots is amino acid 394 in exon 0 (R394W), which occurs in 40% of the DDS patients. A number of kidney- and gonadal-specific targets of WT1 have identified, and are likely to be critical components in the development of the DDS phenotypes. To determine whether the R394W mutation will cause the DDS phenotypes in mice as seen in human, a mouse model containing an arg to trp substitution at codon 394 will be generated using PCR site-directed mutage4nesis and the cre-lox gene-targeting strategies. The effects of this mutation on genitourinary (GU) development will be assessed by examination of gross morphological phenotypes. In addition, the role of this mutation in the development of DDS will be studied by in situ hybridization and immunohistochemistry by determining the effects on the expression of various kidney- and gonadal-development specific molecular markers. If the mutation results in infertility, embryonic lethality or both, DDS chimeric animals will be generated to determine the contribution of the mutant cells in the development of the urogenital organs. Moreover, this study will help to determine if this point mutation in Wt1 causes Wilms' tumor in mice. Susceptibility to tumor development, also will be analyzed after cross- breeding with heterozygous p53 mutant mice. The establishment of a mouse model to analyze DDS will be extremely useful in determining, how a point mutation in WT1 causes a constellation of urogenital effects in patients with DDS.